US20170036327A1 - Electric tool - Google Patents

Abstract

Provided is an impact type electric tool. A striking mechanism is used, which uses a hammer having striking claws that are equally arranged in the rotational direction and an anvil having struck claws. A relationship between a striking energy E, which the hammer has right before striking the anvil, and a disengaging torque T_B, which is applied between the hammer and the anvil right before the hammer is disengaged from the anvil, is set as 5.3×T_B<E<9.3×T_Bin the case of three claws and set as 9.3×T_B<E<15.0×T_Bin the case of two claws, so as to perform striking by skipping one of the claws of the hammer and the anvil when a high torque is required. Accordingly, the electric tool achieves output of a high torque while maintaining a favorable operational feeling during striking.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application claims the priority benefits of Japan application serial no. 2015-157817, filed on Aug. 7, 2015, and Japan application serial no. 2016-070906, filed on Mar. 31, 2016. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.
BACKGROUND OF THE INVENTIONField of the Invention
• The invention relates to an impact type electric tool, in which a hammer is capable of applying a striking force to an anvil in a rotational direction.
Description of Related Art
• Conventionally, an electric tool is known as a device for transmitting a rotational force of a motor to a hammer so as to apply a striking force in the rotational direction to an anvil through the hammer. The impact tool disclosed in Japanese Patent Publication No. S59-88264 is one example. The impact tool is widely used for works such as fastening screw members into lumber or fixing bolts into concrete, loosening screw members or bolts, and so on. When a trigger of a trigger switch is pulled, a motor in the impact tool is driven to rotate a spindle via a speed reduction mechanism. As the spindle is rotated, the hammer connected to the spindle by a hammer spring and cam balls rotates. When the hammer rotates, a rotational force is transmitted through striking claws of the hammer and blade parts of the anvil to rotate the anvil. An end of the anvil in the axial direction is formed with a mounting hole for mounting a tip tool. A screw or bolt can be fastened by using the tip tool, e.g. a hexagonal bit, mounted in the mounting hole.
• In the case of performing the fastening process on lumber, drywall screw is used, for example. When the impact tool is used to fasten the drywall screw, the hammer and the anvil rotate synchronously (continuous rotation) for a little while after the fastening begins. Then, a counter torque generated by the drywall screw increases gradually as the fastening proceeds, and when the counter torque exceeds the spring pressure of the hammer spring, the hammer gradually compresses the hammer spring and gradually retreats to the motor side along the shapes of spindle cam grooves and hammer cam grooves. Because of the retreat of the hammer, a contact length of the striking claws of the hammer and the struck claws of the anvil in the front-rear direction is decreasing. When the contact length of the striking claws of the hammer and the struck claws of the anvil in the front-rear direction becomes 0 mm, the hammer engaged with the anvil with respect to the rotational direction is disengaged therefrom. The value of the torque applied between the hammer and the anvil right before the disengagement is a “disengaging torque” at the time the hammer and the anvil disengage from each other.
• When the counter force from the drywall screw exceeds the disengaging torque, the striking claws of the hammer move over the struck claws of the anvil and then the hammer becomes engaged (or collides) with the next struck claw of the anvil as being pushed out to the side of the hexagonal bit by the compression force of the hammer spring. The striking claws on the hammer and the blade parts on the anvil repeat the operation of disengagement and engagement (striking operation) till the fastening of the drywall screw is completed. As the drywall screw is fastened into the lumber, the counter torque from the drywall screw increases gradually, which also raises the hammer back amount. The reason is that the rate of repulsion that occurs between the hammer and the anvil increases with the counter torque generated by the drywall screw.
PRIOR ART LITERATUREPatent Literature
• Patent Literature 1: Japanese Patent Publication No. S59-88264
SUMMARY OF THE INVENTIONProblem to be Solved
• In recent years, high-torque impact tools have been realized and products that output a fastening torque of 150N·m or more are also available in the market. In order to increase the fastening torque of impact tools, a spring constant of the spring for pushing the hammer toward the anvil side is set high. However, the inventors found that, if the spring constant of the spring is increased to achieve high output power, the disengaging torque also increases and the following problems occur.
• The timing of transition from continuous rotation to the striking operation is delayed when the disengaging torque increases. Thus, the counter torque applied on the impact tool increases and makes it difficult for the operator to hold the impact tool in one hand to fasten screws. Moreover, in the case of fastening screws into soft wood or the like that does not require a high fastening torque, the impact tool with the increased spring constant may not reach the disengaging torque in the screw fastening operation, which results in the problem that the striking operation is hard to carry out. If the striking operation could not be performed, the screw threads of the tip tool may easily float from the cross groove of the drywall screw and the hexagonal bit may come off and be repelled. In that case, the tip tool rotates idly and damages the screw head of the drywall screw. In this way, the impact tool does not perform its characteristics when the disengaging torque is too high and particularly the effect of preventing cam-out is not achieved.
• In view of the above background, the invention provides an impact type electric tool that suppresses increase of the disengaging torque of the hammer and the anvil and enhances the striking force in the rotational direction to achieve high output power as well as allows the operator to carry out the screw fastening operation by holding the electric tool in one hand.
• The invention also provides an electric tool that achieves high output power as well as improves the operation feeling during transition from continuous rotation to striking. The invention further provides an electric tool, in which the hammer striking claw strikes the struck claw following the next struck claw of the anvil to ensure a sufficient fastening torque without increasing the spring constant of the hammer spring.
Solution to the Problem
• The invention is described as follows. According to a feature of the invention, an electric tool includes a motor, a spindle that is driven in a rotational direction by the motor, a hammer that is relatively movable in an axial direction and the rotational direction in a predetermined range with respect to the spindle and urged forward by a cam mechanism and a spring, and an anvil that is disposed rotatably in front of the hammer to be struck by the hammer when the hammer rotates while moving forward. The hammer has three striking claws that are arranged equally in the rotational direction and the anvil has three struck claws that are arranged equally in the rotational direction. A striking operation is performed in a range that a relationship between a striking energy E, which the hammer has right before the hammer strikes the anvil, and a disengaging torque T_B, which is applied between the hammer and the anvil right before the hammer is disengaged from the anvil, is set as E>5.3×T_B. Moreover, when striking is performed in the range of the disengaging torque T_B, a range of a relative rotation angle of the hammer with respect to the anvil from when the hammer strikes the anvil till the hammer strikes the anvil again after the hammer stroke the anvil and moved rearward is set to substantially 240 degrees, and a revolution speed of the motor is controlled to carry out “one-skip striking” that the striking claw moves over the next struck claw to strike the struck claw following the next struck claw. The revolution speed is a revolution speed when a trigger is pulled to the maximum or to a state close to the maximum. In this configuration, a striking timing is improved even if the practical revolution speed of the spindle is set to 2,300 rpm or more, and a fastening torque is sufficiently enhanced while a ratio of the disengaging torque to the striking energy is small. Additionally, in contrast to the increasing fastening torque, the disengaging torque remains equal to the conventional torque. Therefore, like the conventional product, a high-output screw fastening process can be performed with one hand.
• According to another feature of the invention, an upper limit of the striking energy E is set as 9.3×T_B>E. By restricting the disengaging torque T_Bin this way, the so-called “one-skip striking” is carried out at a favorable timing. Here, preferably a diameter of the hammer is 35 mm-44 mm, an inertia of the hammer is 0.39 kg·cm²[0.00038N·m²] or less, a diameter of the spindle is 10 mm-15 mm, and a spring constant of the spring is 37 kgf/cm or less. In addition, when a maximum engagement amount, which is an engagement length of the anvil and the hammer in the axial direction when the anvil is at a foremost position, is set to A [mm] and a cam lead angle, which is a lead angle between cams disposed on the hammer and the spindle such that the hammer retreats when the hammer rotates relatively with respect to the spindle, is set to θ [deg], a relationship between A and θ is set as (−0.125×θ+7.5)−0.7<A<(−0.125×θ+7.5)+0.7. When the relational equation is satisfied, the timing from continuous rotation of the hammer to the start of the striking operation is improved.
• According to another feature of the invention, an overlapping length of the striking claws and the struck claws in the axial direction when a counter torque received from a tip tool mounted on the anvil is small is 2.3 mm-5.0 mm, and the lead angles θ of a cam groove of the hammer and a cam groove of the spindle are made equal and set as θ=26-36 degrees. In this configuration, a rotation speed of the spindle is adjusted such that the striking claw strikes the next struck claw, or to perform the one-skip striking that the striking claw moves over the next struck claw to strike the struck claw following the next struck claw when the hammer retreats to disengage the striking claw from the struck claw and rotates.
• According to yet another feature of the invention, in an impact type electric tool, a hammer has two striking claws while an anvil has two struck claws. A striking operation is performed in a range that a relationship between a striking energy E, which the hammer has right before the hammer strikes the anvil, and a disengaging torque T_B, which is applied between the hammer and the anvil right before the hammer is disengaged from the anvil, is set as 9.3×T_B<E<15.0×T_B. Moreover, when striking is performed in the range of the disengaging torque T_B, a range of a relative rotation angle of the hammer with respect to the anvil from when the hammer strikes the anvil till the hammer strikes the anvil again after the hammer stroke the anvil and moved rearward is set to substantially 360 degrees, and a revolution speed of the motor is controlled to carry out “one-skip striking” that the striking claw moves over the next struck claw to strike the struck claw following the next struck claw. The revolution speed is a revolution speed when the trigger is pulled to the maximum or in a state close to the maximum. In this configuration, a striking timing is improved even if the practical revolution speed of the spindle is set to 2,100 rpm or more, and a fastening torque is sufficiently enhanced while a ratio of the disengaging torque to the striking energy is small.
• The aforementioned and other features of the invention can be understood through the description of the specification and the figures below.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a longitudinal cross-sectional view showing the internal structure of theimpact tool1 according to an embodiment of the invention.
• FIG. 2 is a partially enlarged view of the striking mechanism part ofFIG. 1.
• FIG. 3(1) andFIG. 3(2) are front view and longitudinal cross-sectional view of theanvil60 ofFIG. 1.
• FIG. 4(1) andFIG. 4(2) are front view and longitudinal cross-sectional view of thehammer40 ofFIG. 1.
• FIG. 5(1) andFIG. 5(2) are front view and side view of thespindle30 ofFIG. 1.
• FIG. 6(1) andFIG. 6(2) are views for illustrating the striking angle during one-skip striking of thehammer40 and theanvil60 ofFIG. 1.
• FIG. 7 is a diagram showing the striking condition based on the striking angle ofFIG. 6(1) andFIG. 6(2).
• FIG. 8(1) andFIG. 8(2) are views for illustrating the striking angle during continuous striking of thehammer40 and theanvil60 ofFIG. 1.
• FIG. 9 is a diagram showing the striking condition based on the striking angle ofFIG. 8(1) andFIG. 8(2).
• FIG. 10 is a diagram showing the relationship between the striking energy and the disengaging torque of theimpact tool1 according to an embodiment of the invention.
• FIG. 11 is a diagram showing the relationship between the maximum engagement amount A and the cam lead angle θ of theimpact tool1 according to an embodiment of the invention.
• FIG. 12 is a longitudinal cross-sectional view showing the internal structure of theimpact tool101 according to the second embodiment of the invention.
• FIG. 13(1) andFIG. 13(2) are partially enlarged views of the striking mechanism part ofFIG. 12, whereinFIG. 13(1) is a cross-sectional view andFIG. 13(2) is a side view.
• FIG. 14(1) andFIG. 14(2) are front view and longitudinal cross-sectional view of theanvil160 ofFIG. 12.
• FIG. 15(1) andFIG. 15(2) are front view and longitudinal cross-sectional view of thehammer140 ofFIG. 12.
• FIG. 16(1),FIG. 16(2), andFIG. 16(3) are front view, side view, and cross-sectional view of thespindle130 ofFIG. 12.
• FIG. 17(1) andFIG. 17(2) are views for illustrating the striking angle during one-skip striking of thehammer140 and theanvil160 ofFIG. 12.
• FIG. 18 is a diagram showing the striking condition based on the striking angle ofFIG. 17(1) andFIG. 17(2).
• FIG. 19(1) andFIG. 19(2) are views for illustrating the striking angle during continuous striking of thehammer140 and theanvil160 ofFIG. 12.
• FIG. 20 is a diagram showing the striking condition based on the striking angle ofFIG. 19(1) andFIG. 19(2).
• FIG. 21 is a diagram showing the relationship between the striking energy and the disengaging torque of theimpact tool101 according to the second embodiment.
• FIG. 22 is a diagram showing the relationship between the maximum engagement amount F and the cam lead angle θ₁of theimpact tool101 according to the second embodiment.
DESCRIPTION OF THEEMBODIMENTSEmbodiment 1
• Hereinafter, embodiments of the invention are described with reference to the figures. In the following description, the vertical direction and the front-rear direction refer to the directions shown in the figures. This embodiment illustrates an impact tool as an embodiment of the electric tool.
• FIG. 1 is a longitudinal cross-sectional view showing the internal structure of animpact tool1 according to an embodiment of the invention. A housing of theimpact tool1 includes abody housing2 and ahammer case3 disposed therein. Theimpact tool1 uses arechargeable battery10 as a power source and amotor4 as a driving source to drive a rotational striking mechanism. A rotational force and a striking force from the striking mechanism are applied to ananvil60 that serves as an output shaft, and the rotational striking force is continuously or intermittently transmitted to a tip tool (not shown), such as a driver bit, held in a mountinghole61aformed on abit holding part70, so as to carry out an operation of fastening screws or bolts.
• The brushless DC (direct current)type motor4 is housed in acylindrical body part2aof thebody housing2 that has a substantially T shape in a side view. Arotation shaft4cof themotor4 is disposed such that an axis A1 thereof extends in a longitudinal direction of thebody part2a. Arotor4ais for forming a magnetic path that is formed by a permanent magnet and includes a laminated core, e.g., a thin metal plate, and a cylindrical permanent magnet is disposed on the outer peripheral side of the laminated core. Astator core4bis formed by a laminated core and has a plurality of pole pieces that protrude radially inward, and a coil of predetermined turns is wound on each of the pole pieces. Y connection can be adopted for connecting the coil, for example. On the rear side of themotor4 in the axial direction and behind thestator core4b, aninverter circuit board5 is disposed for driving themotor4. Theinverter circuit board5 is a substantially annular double-sided substrate, wherein a plurality of switchingelements15, e.g., field effect transistor (FET), are mounted on the rear side of the substrate and a plurality of rotationalposition detecting elements16, e.g., Hall IC, are mounted on the front side at predetermined intervals at positions opposite to the permanent magnet of therotor4a. A coolingfan13 is disposed on therotation shaft4con the front side of themotor4 to rotate in synchronization with themotor4. External air is sucked throughair inlets17 and18 on the rear of thebody housing2 by rotation of the coolingfan13 to cool themotor4 or theswitching elements15 and then discharged outside through an air outlet (not shown) formed around the coolingfan13.
• A trigger switch6 is disposed in the upper portion of ahandle part2bthat extends integrally and substantially orthogonally from thebody part2aof thebody housing2. Atrigger6athat serves as an operating lever is exposed to the front side of thebody housing2 from the trigger switch6. In addition, a forward-reverse switching lever7 for switching the rotational direction of themotor4 is disposed above the trigger switch6. Anenlarged diameter part2cis formed in the lower portion of thehandle part2bfor attaching thebattery10. Theenlarged diameter part2cis a part formed to expand radially (orthogonal direction) from a longitudinal central axis of thehandle part2b, and thebattery10 is mounted on the lower side of theenlarged diameter part2c. In theenlarged diameter part2c, a control circuit board (not shown) is housed which has a function of controlling the speed of themotor4 according to an operation of pulling thetrigger6a. The control circuit board is disposed to be substantially horizontal. A microcomputer (also referred to as “MCU” hereinafter) is mounted on the control circuit board. In addition, a changeover switch9 for changing the operation mode is provided on a side surface of theenlarged diameter part2c. A secondary battery such as nickel hydrogen battery or lithium ion battery is used as thebattery10, and a battery pack that contains a plurality of cells in a battery housing is used.
• FIG. 2 is a partially enlarged view that illustrates the power transmission mechanism part between therotation shaft4cof themotor4 and the mountinghole61aofFIG. 1. The rotational driving force of themotor4 is transmitted from therotation shaft4cto the side of the rotational striking mechanism via aspeed reduction mechanism20 that uses planetary gears. Thespeed reduction mechanism20 transmits the output of themotor4 to aspindle30. Here, the speed reduction mechanism that uses planetary gears is adopted. Thespeed reduction mechanism20 includes asun gear21 fixed to an end of therotation shaft4cof themotor4, aring gear23 disposed to surround thesun gear21 at a distance on the outer peripheral side, and a plurality of planetary gears22 (here, the number is three) disposed between and engaged with thesun gear21 and thering gear23. The threeplanetary gears22 revolve around thesun gear21 while rotating around shafts24a-24c(24cis not shown) respectively. Thering gear23 is fixed to the side of thebody housing2 and does not rotate. The shafts24a-24c(as described below with reference toFIG. 2) are fixed to planetary carrier parts (attachment parts37 and38) that are formed on a rear end portion of thespindle30. The revolution motion of theplanetary gears22 is converted into the rotational motion of the planetary carrier parts to rotate thespindle30.
• Thespindle30 is disposed on the front side coaxially with thespeed reduction mechanism20. In this embodiment, on the rear side of a columnarspindle shaft part31 wherespindle cam grooves33 and34 are formed, the planetary carrier parts of thespeed reduction mechanism20 are connected and these are manufactured integrally from a piece of metal. On an end of thespindle30 on the side of themotor4, acylindrical hole35arecessed toward the front side in a direction along the axis A1 is formed to serve as a housing space of thesun gear21. Further, on an end of thespindle30 on the side of theanvil60, a cylindricalfitting hole31ais formed to be recessed rearward along the axis A1.
• Thehammer40 is mounted from the front side (left side of the figure) of thespindle30 and is disposed such that the outer peripheral surface of the shaft part of thespindle30 and a portion of the inner peripheral surface of thehammer40 on the rear side are in contact with each other. On the outer peripheral surface of the cylindrical portion of thespindle30, thespindle cam grooves33 and34 are formed, which are recessed portions having a substantially V shape in the side view of thespindle30.Hammer cam grooves44 and45 are formed on the inner peripheral surface of thehammer40 opposite to thespindle cam grooves33 and34. Thespindle30 and thehammer40 are combined in a way that a predetermined space is formed by thespindle cam grooves33 and34 and thehammer cam grooves44 and45.Metallic cam balls51aand51bare disposed in the space, so as to form a cam mechanism. The cam mechanism allows thehammer40 to rotate substantially in linkage with thespindle30. Thecam balls51aand51bmove in the space, by which the relative positions of thehammer40 and thespindle30 in the rotational direction change slightly. Thehammer40 is slightly movable with respect to thespindle30 in the axial direction and is movable to a large extent toward the rear side. Moreover, because thehammer40 is constantly urged toward the front side with respect to thespindle30 by thespring54, rearward movement of thehammer40 will compress thespring54.
• When thespindle30 is stationary, due to the balance relationship between the engagement positions of thecam balls51aand51b, thespindle cam grooves33 and34, and thehammer cam grooves44 and45 and the urging force with respect to thespring54, afront surface42aof thehammer40 and the rear end surface of the claw part of theanvil60 are at positions spaced by a slight gap in the axial direction. Meanwhile, theblade part63aof theanvil60 and thestriking claw46aof thehammer40 are in a positional relationship that they overlap each other in the direction of the axis A1, and a length of the engagement in the axial direction is an engagement amount A. Here, the engagement amount A is an axial length of a contact area of the striking claws46a-46cof thehammer40 and the blade parts63a-63cof theanvil60 when viewed in the direction of the axis A1, and as shown inFIG. 2, the engagement amount A has a maximum value when they are stationary or at the initial positions before striking. The engagement amount A changes according to the rearward movement of thehammer40, and when the counter torque transmitted to thehammer40 increases due to the force that theanvil60 receives from the tip tool side, the positions of thecam balls51aand51bmove and cause the relative positional relationship between thehammer40 and theanvil60 to change.
• Thespring54 is a compression spring. On the front side of thespring54, a plurality ofsteel balls52 are disposed in a state of being pressed by awasher53, and the rear side of thespring54 is fixed on a stepped part36 (refer toFIG. 5(2)) of thespindle30 by a steppedwasher55. On the inner peripheral side of thewasher55, anannular damper56 is disposed, which is formed for thespindle30 to pass through in the center. Thedamper56 is composed of an elastic material such as rubber and prevents direct collision with thespeed reduction mechanism20 when thehammer40 retreats to the maximum extent and thereby alleviates the impact when thecam balls51aand51bcollide with the ends of thespindle cam grooves33 and34 and the ends of thehammer cam grooves44 and45.
• The striking mechanism and the speed reduction mechanism including and composed of thespindle30, thehammer40, and theanvil60 are disposed in a way that the rotation centers of thespindle30, thehammer40, and theanvil60 line up along the axis A1, and are housed inside the taperedmetallic hammer case3 and fixed to the front side of thebody housing2. The assembly shown inFIG. 2 is pivotally supported in thehammer case3 by ametal19aat the front side and pivotally supported in thebody housing2 via abearing19band a bearing holder8 (refer toFIG. 1) at the rear side.
• Next, a shape of theanvil60 is described with reference toFIG. 3(1) andFIG. 3(2).FIG. 3(1) is a front view of theanvil60 andFIG. 3(2) is a cross-sectional view along the section B-B. Here, please note that, to facilitate understanding of the invention,FIG. 3(2) is a cross-sectional view along the section B-B ofFIG. 3(1). Moreover, only theanvil60 and the struck claws, the striking claw portion of thehammer40, and theplanetary gears22 of the speed reduction mechanism in the cross-sectional views ofFIG. 1 andFIG. 2 are shown in the cross-sectional view along the section B-B. Theimpact tool1 needs to be designed such that the striking claws of thehammer40 do not pre hit or over shoot the blade parts of theanvil60 when the engaging parts (the striking claws and the struck claws) provided on thehammer40 and theanvil60 are repeatedly disengaged from and engaged with one another. The reason is that if pre hit or over shoot occurs, theimpact tool1 may vibrate greatly and cause the performance to drop significantly. In order to prevent the aforementioned problem, generally the number of the hammer claws and the number of the blade parts of the anvil in theconventional impact tool1 are both two. If the number of the striking claws is three or more, the rotation angle will be 180 degrees or less. Consequently, pre hit is likely to occur. On the other hand, if the number of the striking claws is one, the rotation angle will be 360 degrees and over shoot may occur easily, and a hammer back amount also needs to be increased. The foregoing is an obstacle to achieving a compact product. According to this embodiment, the number of the striking claws of thehammer40 and the number of the blade parts of theanvil60 are both set to three and thespindle30 is controlled in a predetermined speed range, so as to achieve smooth transition from continuous rotation to striking as well as realize a high-torque impact tool.
• Theanvil60 is manufactured integrally from a piece of metal, wherein astruck part62 with three blade parts63a-63cis formed at the rear of a cylindricaloutput shaft part61 of theanvil60. The mountinghole61ahaving a hexagonal cross-sectional shape is formed into an inner portion of theoutput shaft part61 from a front end part for mounting the tip tool. Two throughholes61bare formed to penetrate theoutput shaft part61 in the radial direction in the middle of the portion where the mountinghole61ais formed in the front-rear direction, and metal balls69 (refer toFIG. 1) are disposed therein to serve as components of thebit holding part70. The outer peripheral surface between the throughholes61band the struck part62 (the portion indicated by thearrow61c) is formed into a columnar shape when viewed in the axial direction. Themetal19a(refer toFIG. 1) is disposed on the outer peripheral side of this region to pivotally support theanvil60 in thehammer case3 in a rotatable manner (refer toFIG. 1). The three blade parts63a-63cof thestruck part62 are struck claws that are arranged at equal intervals of 120 degrees when viewed in the rotational direction and extend outward in the radial direction. On side surfaces of the blade parts63a-63cin the rotational direction, struck surfaces64a-64cand struck surfaces65a-65care formed, wherein the struck surfaces64a-64care to be struck by the striking claws of thehammer40 during rotation in a fastening direction, and the struck surfaces65a-65care formed on the opposite sides to be struck during rotation in a loosening direction. Acylindrical shaft part66 is formed on the rear side of thestruck part62, and the outer peripheral surface of theshaft part66 is pivotally supported by thefitting hole31aof thespindle30 in a slidable manner (refer toFIG. 2).
• Next, a shape of thehammer40 is described with reference toFIG. 4(1) andFIG. 4(2).FIG. 4(1) is a front view of thehammer40 andFIG. 4(2) is a cross-sectional view along the section C-C. As shown inFIG. 4(2), thehammer40 has a shape that front sides of twocylindrical portions41 and43 that have different inner diameters are connected by aconnection part42 in the radial direction. Here, thehammer40 is made of a metal. Thehammer40 may be configured to have a diameter (outer diameter) of about 35-44 mm and an inertia of 0.39 kg·cm²[0.00038N·m²] or less. The three striking claws46a-46cthat protrude toward the front side (the side of the anvil60) in the axial direction are formed at three positions on the outer peripheral side of thefront surface42awhich is formed by theconnection part42. As shown inFIG. 4(1), the striking claws46a-46care equally arranged in a way that the central positions of the striking claws46a-46care respectively separated by a rotation angle of 120 degrees when viewed in the rotational direction. Two side surfaces of each of the striking claws46a-46cin the rotational direction are arranged at predetermined angles in the rotational direction to achieve proper surface contact when colliding with the three blade parts63a-63cof theanvil60. Thehammer cam grooves44 and45 are formed on the inner peripheral side of thecylindrical portion41 of the hammer and on an inner wall portion of a throughhole41awhich faces the outer surface (cylindrical surface) of thespindle30. Thehammer cam grooves44 and45 are recesses, which respectively have a substantially trapezoidal contour if the inner peripheral surface of thehammer40 is unfolded into a plane, and form a space that restricts movement of thecam balls51aand51bwith thespindle cam grooves33 and34. In addition,grooves44aand45afor inserting thecam balls51aand51bduring assembly are formed on a portion of thehammer cam grooves44 and45. In this embodiment, a cam lead angle θ_Hof thehammer40 is set within a range, e.g., θ_H=26-36 degrees, for example, to make the cam lead angle θ_Ha predetermined value.
• Next, a shape of thespindle30 is described with reference toFIG. 5(1) andFIG. 5(2).FIG. 5(1) is a front view of thespindle30 andFIG. 5(2) is a side view. Thespindle30 is disposed coaxially with the axis A1 between theanvil60 and thespeed reduction mechanism20 and arear end part39 of thespindle30 in the longitudinal direction is pivotally supported by the bearing19b(refer toFIG. 1). Thespindle30 is made of a metal and a diameter d of theshaft part31 may be about 10-15 mm. The bearing19bis fixed to thebody housing2 via the bearing holder8 (refer toFIG. 1). The twospindle cam grooves33 and34 are formed on the outer peripheral surface of thespindle30. Here, thespindle cam groove33 is separated from thespindle cam groove34 by an angle of 180 degrees in the rotational direction and therefore cannot be seen inFIG. 5(2), but thespindle cam groove33 has the same shape as thespindle cam groove34. Thespindle cam grooves33 and34 respectively have a substantially V shape in the side view (when viewed in an upper direction orthogonal to the axis A1), and a cam lead angle θ_Sof each of thespindle cam grooves33 and34 is set to a predetermined angle. In this embodiment, the cam lead angle θ_Hof thehammer40 and the cam lead angle θ_Sof thespindle30 are set to be the same in the range of 26-36 degrees, for example. The disengaging torque and a maximum current during practical use rise as the cam lead angles θ_Hand θ_Sincrease; on the other hand, the disengaging torque and the maximum current during practical use both drop as the cam lead angles θ_Hand θ_Sdecrease. Thus, maintaining a balance between the foregoing is important.
• Aplanetary carrier part35 of thespeed reduction mechanism20 is formed and theattachment parts37 and38 are formed on the rear side of the columnarspindle shaft part31. Theattachment part37 extends to be orthogonal to the axis A1 and is formed with threefitting holes37a-37cthat are arranged at equal intervals in the rotational direction. Theattachment part38 is disposed in parallel to theattachment part37 on the rear side at a predetermined distance from theattachment part37. Theattachment part38 is also formed with three fitting holes (not shown) that are arranged at equal intervals in the rotational direction and fix the shafts24a-24c(also refer toFIG. 2), which pivotally support theplanetary gears22 with thefitting holes37a-37cof theattachment part37. The steppedpart36 having an increased thickness in the axial direction is formed on the front side of theattachment part37.
• When thetrigger6ais pulled to activate themotor4, themotor4 starts to rotate in the direction set by the forward-reverse switching lever7 and the rotational force is reduced at a predetermined reduction ratio by thespeed reduction mechanism20 and transmitted to thespindle30 to drive thespindle30 to rotate at a predetermined speed. Here, thespindle30 and thehammer40 are connected by the cam mechanism, and when thespindle30 is driven to rotate, the rotation is transmitted to thehammer40 via the cam mechanism. When the rotation begins and before thehammer40 reaches ⅓ of the rotation, the striking claws46a-46cof thehammer40 abut against the blade parts63a-63cof theanvil60 and cause theanvil60 to rotate. At the moment, when the engagement counter force from theanvil60 causes relative rotation between thespindle30 and thehammer40, thehammer40 starts to retreat toward the side of themotor4 while compressing thespring54 along thespindle cam grooves33 and34 of the cam mechanism. Then, when the striking claws46a-46cof thehammer40 move over the blade parts63a-63cof theanvil60 due to the retreat of thehammer40 to release thehammer40 and theanvil60 from the engagement state, thehammer40 is rapidly accelerated forward and rotated in the rotational direction by the elastic energy accumulated in thespring54 and the function of the cam mechanism in addition to the rotational force of thespindle30.
• When thehammer40 is moved forward by the urging force of thespring54, the striking claws46a-46cof thehammer40 are engaged with the next blade parts63a-63cof theanvil60 again during the rotation, so as to perform strong striking and thehammer40 and theanvil60 start to rotate together. The striking applies a strong rotational force to theanvil60. Thus, a rotational striking force is transmitted to a screw through the tip tool (not shown) which is mounted in the mountinghole61aof theanvil60. Thereafter, the same operation is repeated to intermittently and repeatedly transmit the rotational striking force from the tip tool to the screw, so as to screw the screw into a material to be fastened, e.g., wood (not shown), for example. The above describes a state when thehammer40 performs normal striking on theanvil60. In this embodiment, however, thehammer40 is formed with three striking claws and theanvil60 is formed with three blade parts respectively for performing characteristic striking. The striking is to adopt one of the following to control the striking of thehammer40 on the anvil60: performing one-skip striking by setting the rotation speed of themotor4 to a high-speed region of a predetermined revolution speed T₁or more; or performing continuous striking by setting the rotation speed to a low-speed region of a predetermined revolution speed T₂or less (T₁>T₂). Moreover, in a region where the revolution speed of themotor4 is more than T₂but less than T₁, one-skip striking is not possible and continuous striking may result in over shoot. Therefore, it is preferable not to use the rotation region of T₂-T₁for the striking operation.
• FIG. 6(1) andFIG. 6(2) are views for illustrating a striking angle during one-skip striking of thehammer40 and theanvil60. Theimpact tool1 of this embodiment is configured to perform the so-called “one-skip striking” when a high torque is required. The configuration is that theanvil60 has the blade parts63a-63cas three struck claws and thehammer40 has the striking claws46a-46cas three striking claws. Rotation angles83 and84 indicated by the arrows indicate the relative rotation angles of thehammer40 with respect to theanvil60. Thestriking claw46aof thehammer40 on a rotation side rotates by therotation angle83 to strike theblade part63cafter passing the rear side of theblade part63aof theanvil60. After being disengaged from thestriking claw46aof thehammer40, theblade part63adoes not contact the nextstriking claw46band is engaged with thestriking claw46cfollowing the nextstriking claw46b.At the moment, the rotation angle is about 240 degrees. After the relative rotation of therotation angle83 of thehammer40 is performed, the relative rotation of therotation angle84 is performed. Thestriking claw46aof thehammer40 rotates by therotation angle84 to strike theblade part63bafter passing the rear side of theblade part63c. It is preferable that the rotation portion including therotation angle83 of thehammer40 and the rotation portion including therotation angle84 of the hammer40 (therotation angle83 or84+the rotation angle of the anvil60) are the same angles. However, since thehammer40 and thespindle30 are slightly relatively rotatable in the rotational direction, thehammer40 and theanvil60 may be different in a rotation range of 220-260 degrees.
• FIG. 7 is a diagram showing a condition of thehammer40 and theanvil60 when the striking is performed based on the striking angle ofFIG. 6(1) andFIG. 6(2). The vertical axis indicates the position of thehammer40 in the front-rear direction relative to theanvil60, wherein “+” indicates thehammer40 is on the front side of theanvil60 while “−” indicates thehammer40 is on the rear side of theanvil60, and the value indicates the distance (mm). 0 indicates a front-side position of thestriking claw46aof thehammer40 during rotation in a stationary or low-load state, and at the moment, a front-side position of theblade part63ais 0 as well. The horizontal axis indicates the relative rotation angle of thehammer40 with respect to theanvil60, wherein one round is 360 degrees. Here, the blade parts63a-63care respectively arranged at an interval of 120 degrees. When thetrigger6ais pulled to the full and thespindle30 rotates at a high speed, a predetermined counter force is applied to thestriking claw46aof thehammer40 and when the counter force exceeds the disengaging torque, thehammer40 retreats. When the retreat amount of thehammer40 becomes larger than the maximum engagement amount A with theblade part63a, thestriking claw46aand theblade part63aare released from the engagement state and thestriking claw46arotates and slips through the rear side of theblade part63aand passes the rear side of thenext blade part63bto strike the followingblade part63c(the blade part that comes after the next blade part with respect to theblade part63a). In the diagram, asolid line71 indicates a locus of movement of a corner part of thestriking claw46aon the axial direction front side and the rotational direction front side while a dottedline72 indicates a locus of movement of a corner part of thestriking claw46aon the axial direction front side and the rotational direction rear side. Thus, in order that thestriking claw46askips thenext blade part63bto strike theblade part63cfollowing thenext blade part63bwhen the striking is performed, thespindle30 is rotated at a sufficiently high speed such that thehammer40 that has compressed thespring54 and moved to the rear side passes theblade part63bbefore returning to the axial direction front side. AlthoughFIG. 7 only illustrates thestriking claw46a, the strikingclaws46band46calso perform the one-skip striking in the same manner. Therefore, despite that theimpact tool1 of the invention has a longer striking interval than the conventional impact tool that has two striking claws and two blade parts, theimpact tool1 is able to achieve a high striking torque. Moreover, for carrying out this striking method, the spring force of thespring54 may be set substantially equal to the current products. Therefore, increase of the disengaging torque resulting from enhancement of thespring54 can be suppressed and the impact tool creates a favorable feeling in transition from continuous rotation to the striking state and is easy to use. The spring constant of thespring54 is preferably set to 40 kgf/cm or less, for example.
• FIG. 8(1) andFIG. 8(2) are views for illustrating the striking angle during continuous striking of thehammer40 and theanvil60. Rotation angles 85-87 indicated by the arrows indicate the relative rotation angles of thehammer40 with respect to theanvil60. Theimpact tool1 of this embodiment is configured to perform the so-called “continuous striking” when a high torque is not required, e.g., when a pulling amount of thetrigger6ais small or when a set revolution speed of themotor4 is low. Thestriking claw46aof thehammer40 on the rotation side rotates by therotation angle85 to strike theblade part63bafter passing the rear side of theblade part63aof theanvil60. Then, thestriking claw46arotates by therotation angle86 to strike theblade part63cafter passing the rear side of theblade part63b. Further, thestriking claw46arotates by therotation angle87 to strike theblade part63aafter passing the rear side of theblade part63c. In addition, after being disengaged from thestriking claw46a, theblade part63ais engaged with the nextstriking claw46cof the hammer that has rotated by therotation angle85. At the moment, the rotation angle of thehammer40 with respect to theanvil60 is approximately 120 degrees. After the striking of therotation angle85 is performed, the striking of therotation angle86 is performed and then the striking of therotation angle87 is performed, and in the same manner, the striking of the striking claw of the hammer on the next struck claw is performed. Here, therotation angle85, therotation angle86, and therotation angle87 are preferably the same. However, it should be noted that, because the rotation angles may be set to be different from one another in the rotation range of 100-160 degrees (for example, therotation angle85 may be 110 degrees, therotation angle86 may be 130 degrees, and therotation angle87 may be 120 degrees), the aforementioned “approximately 120 degrees” refers to an angle in a predetermined range.
• FIG. 9 is a diagram showing a condition of thehammer40 and theanvil60 when the striking is performed based on the striking angle ofFIG. 8(1) andFIG. 8(2). The vertical axis and the horizontal axis have the same relationship asFIG. 7. During rotation of thespindle30 in the low-speed mode, a predetermined counter force is applied to thestriking claw46aof thehammer40 and when the predetermined counter force exceeds the disengaging torque, thehammer40 retreats, and when the retreat amount of thehammer40 becomes larger than the maximum engagement amount A with theblade part63a, thestriking claw46aand theblade part63aare released from the engagement condition and thestriking claw46arotates and slips through the rear side of theblade part63aand is engaged with thenext blade part63b. In the diagram, asolid line73 indicates a locus of movement of the corner part of thestriking claw46aon the axial direction front side and the rotational direction front side while a dottedline74 indicates a locus of movement of the corner part of thestriking claw46aon the axial direction front side and the rotational direction rear side. Thus, in order that thestriking claw46ais properly engaged with thenext blade part63bwhen the striking is performed, thespindle30 needs to be rotated at a lower speed than the rotation condition ofFIG. 7, so as to bring thenext blade part63bas thehammer40 that has compressed thespring54 and moved to the rear side returns to the axial direction front side. Therefore, when performing the continuous striking, the control circuit performs rotation control on themotor4 so as to rotate thespindle30 at a low rotation speed for properly carrying out the continuous striking. AlthoughFIG. 9 only illustrates thestriking claw46a, the strikingclaws46band46calso perform the continuous striking in the same manner. Since the striking interval at the moment is shorter than the striking interval of the conventional impact tool that has two striking claws and two blade parts, the striking torque decreases correspondingly. Thus, in the case of fastening a drywall screw or the like into soft wood, the striking can be reliably carried out by the striking mode, and therefore the impact tool is easy to use.
• FIG. 10 is a diagram showing a relationship between striking energy and the disengaging torque of theimpact tool1 of this embodiment. The striking energy E is the energy that thehammer40 has right before thehammer40 strikes theanvil60. Here, it is calculated based on the conditions that the operation amount (pulling amount) of thetrigger6ais at the maximum, the material to be fastened is lauan material (wood), and the repulsion rate is 0.31. The disengaging torque T_B[kg·cm] and the striking energy E [N·m²×(rad/s)²] shown here are values obtained by thefollowing equation 1 andequation 2.
• 
  Disengaging torqueT_B[kg·cm]=spring constant [kg/cm]×(spring pressing height) [cm]×tan(cam lead angle [deg]×cam contact radius [cm])   Equation 1:
• However, the spring pressing height [cm] is a value obtained by subtracting the spring height [cm] at the time of disengagement from the free length [cm] of the spring (1.1 cm in this embodiment).
• The cam lead angle θ [deg] is θ_H[deg] and θ_S[deg].
• The cam contact radius [cm] is a distance from the central axis of thespindle30 to the center point of the R shape of the cam (the arc notch of the cam) formed in the spindle (0.7 cm in this embodiment). The disengaging torque T_Bshown here indicates a disengaging torque in the stationary state and may be easily obtained based on the respective dimensions of the aforementioned parts.
• 
  Striking energyE[N·m²×(rad/s)²]=0.5×hammer inertia [N·m²]×(speed right before hammer striking [rad/s])²  Equation 2:
• However, the speed right before hammer striking [rad/s]=spindle angular speed [rad/s]+(spindle angular speed [rad/s]×a coefficient considering the repulsion rate)
• 
  Spindle angular speed [rad/s]=2×π×spindle revolution speed [rps]
• The coefficient considering the repulsion rate is 1.9 in this embodiment.
• Furthermore, the spindle revolution speed shown here indicates the spindle revolution speed during the screw fastening operation. If the practical revolution speed of therotor4aduring the screw fastening operation is to be verified, it may be easily obtained based on the reduction ratio of the planetary gears. In addition, the coefficient considering the repulsion rate varies according to the hardness of the wood.FIG. 10 as described below shows the striking energy E based on the aforementioned values.
• The plot points shown inFIG. 10 are obtained by respectively plotting the striking specifications of the invention and the conventional technology.FIG. 10 shows the striking energy E and the disengaging torque T_Bin the case where the rotation angle till engagement of thestriking claw46aof the hammer with thenext blade part63bof the anvil after disengagement of thestriking claw46afrom theblade part63ais set to 120 degrees, and the range of a coefficient K are represented as an upper limit coefficient K₂and a lower limit coefficient K₁.A plot group91 indicates the relationship between the striking energy E and the disengaging torque T_Bof the current product available in the market. According to the conventional technology, in order to further enhance the striking energy E, the spring pressure of thespring54 needs to be increased and consequently the disengaging torque T_Bincreases as well. The reason is that, as shown inequation 2, when the rotation speed of thespindle30, which is the most influential factor, is raised to enhance the striking energy, the spring constant needs to be increased considering the purpose of achieving proper striking timing within the rotation angle of 180 degrees. Nevertheless, if the spring pressure of thespring54 increases, the disengaging torque T_Bin the lower region of the solid line K₁increases and exceeds the practical upper limit, i.e., T_B=20 kg·cm, which will impair the practicality.
• In contrast thereto, in the case when the rotation angle of the impact tool is such that the rotation angle till engagement with thenext blade part63bafter disengagement from theblade part63aof the anvil is 220-260 degrees, the relationship between a coefficient K_Pand the striking energy E and the disengaging torque T_Bof the impact tool is set as E=K_P×T_B[K₁<K_P], as indicated by aplot group92, the striking energy E can be improved significantly while the disengaging torque is maintained at 12-18 kg·cm, and thus it is possible to obtain high striking energy E in the upper region with respect to the region of the solid line K₁. The reason is that, by setting the rotation angle as large as 220-260 degrees, the spindle revolution speed can be increased with an equal or less disengaging torque.
• Thus, the striking mechanism having three striking claws and three struck claws is used in this embodiment to perform striking in the region where the relationship between the striking energy E and the disengaging torque T_Bsatisfies E>5.3×T_B. Meanwhile, setting an appropriate disengaging torque T_Bis also important. For instance, if the disengaging torque T_Bis overly small, there is a risk that the striking operation may be performed even in the fastening operation or drilling operation that requires no striking. On the other hand, if the disengaging torque T_Bis overly large, the counter force from theimpact tool1 may hinder the fastening operation that the operator performs with one hand. According to the results verified by the inventors, one-handed operation is almost impossible in the case of 25 kg·cm or more. Moreover, because practically the upper limit of the disengaging torque T_Bis about 20 kg·cm, the disengaging torque TB is set to about 10-20 kg·cm or more preferably about 12-18 kg·cm.
• Furthermore, the control may be switched to perform the so-called continuous striking, in which the rotation angle till engagement with thesecond blade part63bafter disengagement from thefirst blade part63aof theanvil60 is 100-160 degrees. The relationship with respect to the striking energy E in this case is not shown inFIG. 10. However, the striking energy E substantially equal to or less than theplot group91 can be obtained and therefore it is suitable for fastening particularly short screws into wood.
• FIG. 11 is a diagram showing a relationship between the maximum engagement amount A [mm] and the cam lead angle θ [deg] of theimpact tool1 according to this embodiment of the invention. According to the inventors' experiment, the impact tool that has a high disengaging torque T_Band creates a favorable striking feeling is realized by the striking specification that uses the maximum engagement amount A of the anvil and the hammer calculated based on Equation 3: A [mm]=−0.125×θ [deg]+7.5, with respect to the cam lead angle θ (=θ_H=θ_S). Further, at the moment, by significantly increasing the spindle revolution speed to perform one-skip striking, the striking energy E is enhanced significantly as compared with the conventional technology. In addition, if the spindle revolution speed is significantly reduced during transition to the striking operation to perform continuous striking, the feeling from continuous striking to the start of the striking is improved. Besides, inequation 3, the range of the maximum engagement amount A may be adjusted in a range of ±0.7. The range of the cam lead angle θ (=θ_H=θ_S) at the moment is preferably about 26-36 degrees.
Embodiment 2
• Next, the second embodiment of the invention is described with reference toFIG. 12 toFIG. 22. Thehammer40 described in the first embodiment includes three striking claws. However, the method of carrying out the “one-skip striking” as described in the first embodiment is also applicable to the structure of the conventional impact tool, in which the anvil has two blade parts and the hammer has two striking claws, and the striking claws and the blade parts are respectively at positions separated by an angle of 180 degrees.FIG. 12 is a longitudinal cross-sectional view showing the internal structure of animpact tool101 according to the second embodiment of the invention. Theimpact tool101 has the same basic structure as theimpact tool1 ofFIG. 1, except that the number of the claws of the hammer and the number of the blade parts of the anvil are both two.
• Theimpact tool101 uses abattery110 as a power source and abrushless type motor104 as a driving source to drive a rotational striking mechanism. Themotor104 is a brushless DC motor that includes arotor104aand astator core104b. On the rear of thestator core104b, a plurality of switchingelements115 and aninverter circuit board105 that carries a plurality of rotationalposition detecting elements116 at predetermined intervals are disposed. A coolingfan113 is disposed to arotation shaft104con the front side of themotor104. The output of themotor104 is transmitted to aspindle130 via a speed reduction mechanism and the power is transmitted to ahammer140 and ananvil160 rotated by thespindle130. The foregoing rotational striking mechanism is housed inside ametallic hammer case103 and the internal space thereof is applied with a sufficient amount of grease. Theanvil160 is pivotally supported by ametal119ato be rotatable. Anattachment part161athat has a quadrangular cross-sectional shape perpendicular to an axial direction D1 is formed on an end of theanvil160. Ahole161bis formed on a side surface of theattachment part161a. A tip tool such as hexagonal socket (not shown) is mounted on theattachment part161aand then fixed by inserting a pin (not shown) into thehole161b, so as to perform various operations such as bolt fastening.
• Atrigger switch106 including atrigger106aand a forward-reverse switching lever107 are disposed in the upper portion of ahandle part102bthat extends downward from abody part102aof abody housing102. Anenlarged diameter part102cis formed in the lower end portion of thehandle part102b. In theenlarged diameter part102c, acontrol circuit board109 is housed for control of rotation of themotor104. The control circuit board is disposed to be substantially horizontal and a microcomputer (not shown) is mounted there.
• FIG. 13(1) andFIG. 13(2) are partially enlarged views of the power transmission mechanism part from therotation shaft104cof themotor104 to theattachment part161aofFIG. 12.FIG. 13(1) is a cross-sectional view andFIG. 13(2) is a side view. Because the spindle of the conventional impact tool has a small diameter, the cam lead angle θ needs to be increased to gain the hammer back amount. On the other hand, in order to perform the one-skip striking like the invention, the rotation angle of the two-claw tool should be larger than that of the three-claw tool (the rotation angle of the hammer becomes 360 degrees) and therefore requires an increased hammer back amount. To increase the cam lead angle, however, the axial direction dimension of the spindle needs to be increased. When the front-rear direction dimension of the tool increases or only the lead angle is increased, the disengaging torque increases as well, which impairs the usability. On the other hand, it is also considered to weaken the spring that urges the hammer for the hammer to rotate one round, but by doing so the striking force drops. Therefore, in the second embodiment, the spindle diameter is made larger than the conventional diameter, that is, a large-diameter spindle is used, so as to gain the hammer back amount without increasing the lead angle.
• The rotational driving force of themotor104 is transmitted from therotation shaft104cto the side of the rotational striking mechanism via aspeed reduction mechanism120 that uses planetary gears. Thespeed reduction mechanism120 transmits the output of themotor104 to thespindle130. Here, the speed reduction mechanism that uses planetary gears is adopted. Thespeed reduction mechanism120 includes asun gear121 fixed to an end of therotation shaft104cof themotor104, aring gear123 disposed to surround thesun gear121 at a distance on the outer peripheral side, and a plurality ofplanetary gears122aand122b(here, the number is two) disposed between and engaged with thesun gear121 and thering gear123. The twoplanetary gears122aand122brevolve around thesun gear121 while rotating aroundshafts124aand124brespectively. Thering gear123 is fixed to the side of thebody housing102 and does not rotate. Theshafts124aand124bare fixed to planetary carrier parts (attachment parts137 and138) that are formed on the rear end portion of thespindle130. The revolution motion of theplanetary gears122aand122bis converted into the rotational motion of the planetary carrier parts to rotate thespindle130.
• Spindle cam grooves133 and134 are formed on the outer peripheral side of thecylindrical spindle130, and the planetary carrier parts of thespeed reduction mechanism120 are connected to the rear side. These are manufactured integrally from a piece of metal. An internal space of thespindle130 on the side of themotor104 is acylindrical hole135athat serves as a housing space of thesun gear121 and ashaft part166 of theanvil160 is housed in afitting hole131aon the front side on the side of theanvil160.
• Thehammer140 is mounted from the front side (left side of the figure) of thespindle130 and is disposed such that the outer peripheral surface of the shaft part of thespindle130 and a portion of the inner peripheral surface of thehammer140 on the rear side are in contact with each other. Thespindle cam grooves133 and134 are recessed portions respectively having a substantially V shape in the side view.Hammer cam grooves144 and145 are formed on the inner peripheral surface of thehammer140 opposite to thespindle cam grooves133 and134.Metallic cam balls151aand151bare disposed in a space formed by thespindle cam grooves133 and134 and thehammer cam grooves144 and145. The cam mechanism allows thehammer140 to rotate substantially in linkage with thespindle130. Thecam balls151aand151bmove in the space, by which the relative positions of thehammer140 and thespindle130 in the rotational direction are slightly changeable, and a large rearward movement in the axial direction is possible. Thehammer140 is constantly urged toward the front side by aspring154 disposed on the rear side.
• When thespindle130 is stationary, afront surface142aof thehammer140 and a rear end surface of a claw part of theanvil160 are at positions spaced by a slight gap in the axial direction. Meanwhile, theblade part163aof theanvil160 and thestriking claw146aof thehammer140 are in a positional relationship that they overlap each other when viewed in the direction of the axis D1, and a length of the engagement in the axial direction is an engagement amount F. Here, the engagement amount F is an axial length of a contact area of thestriking claws146aand146bof the hammer140 (refer toFIG. 15(1) andFIG. 15(2)) and theblade parts163aand163bof theanvil160 when viewed in the direction of the axis D1, and as shown inFIG. 13(1) andFIG. 13(2), the engagement amount F has a maximum value when they are stationary or at the initial positions before striking. The engagement amount F changes according to the rearward movement of thehammer140.
• Thespring154 is a compression spring. On the front side of thespring154, a plurality ofsteel balls152 are disposed in a state of being pressed by awasher153, and the rear side of thespring154 is held on theattachment part137 of thespindle130 by awasher155 having an inner peripheral side that extends in the axial direction to form a cylindrical shape and an outer peripheral side that is annular. Adamper156 composed of a cylindrical elastic body is disposed between the cylindrical portion of thewasher155 and thespindle130. A rotation body of theanvil160, thehammer140, and thespindle130 as shown inFIG. 13(1) is pivotally supported in thehammer case103 by ametal119a(refer toFIG. 12) on thecylindrical surface161con the front side and is pivotally supported on a bearing holder108 (refer toFIG. 13(1) andFIG. 13(2)) by abearing119bon the outer peripheral surface of the rear side end. An annular gap portion that is continuous in the circumferential direction is formed on an outer peripheral side joint of thering gear123 and thebearing holder108, and anO ring129 is interposed there. The space in the hammer case103 (refer toFIG. 12) on the front side with respect to theO ring129 is applied with a sufficient amount of grease or the like.
• FIG. 14(1) is a front view of theanvil160 andFIG. 14(2) is a cross-sectional view along the section G-G ofFIG. 14(1). In the first embodiment described above, the number of the claws of thehammer40 and the number of the blade parts of theanvil60 are both three so as to realize two operation modes, i.e., performing one-skip striking by setting the rotation speed of themotor4 to the high-speed region of the predetermined revolution speed or more, and performing continuous striking by setting the rotation speed to the low-speed region of the predetermined revolution speed or less. In the second embodiment, however, the one-skip striking and continuous striking are realized by the impact tool that the number of the claws of thehammer140 and the number of the blade parts of theanvil160 are both two. If the revolution speed of thespindle130 is in the predetermined speed region or less, continuous striking is performed in the same manner as the conventional impact tool. However, by skipping the predetermined speed region (intermediate speed region) and rotating themotor4 in the even faster high-speed region, the fastening operation of “one-skip striking” is also possible.
• Theanvil160 is manufactured integrally from a piece of metal, wherein astruck part162 with theblade parts163aand163bis formed at the rear of a cylindricaloutput shaft part161, as shown inFIG. 14(2). The outerperipheral surface161csubstantially near the center when viewed in the axial direction is formed into a columnar shape. Anoil supply hole167 including an axial direction groove167band a radial direction groove167ais formed on theanvil160 for supplying grease to themetal119afrom the side of anopening167c. Theoil supply hole167 may be formed by drilling in the radial direction and the axial direction with use of a drill. The twoblade parts163aand163bof thestruck part162 are struck claws that are separated by an angle of 180 degrees when viewed in the rotational direction and extend outward in the radial direction. On side surfaces of theblade parts163aand163bin the rotational direction, strucksurfaces164aand164band strucksurfaces165aand165bare formed, wherein the strucksurfaces164aand164bare to be struck by the striking claws of thehammer140 during rotation in the fastening direction, and thestruck surfaces165aand165bare formed on the opposite sides to be struck during rotation in the loosening direction. Acolumnar shaft part166 is formed on the axial direction rear side of thestruck part162, and the outer peripheral surface of theshaft part166 is pivotally supported by thefitting hole131aof thespindle130 in a slidable manner (refer toFIG. 13(1) andFIG. 13(2)).
• Next, a shape of thehammer140 is described with reference toFIG. 15(1) andFIG. 15(2).FIG. 15(1) is a front view of thehammer140 andFIG. 15(2) is a cross-sectional view along the section H-H ofFIG. 15(1). As shown inFIG. 15(2), thehammer140 has a shape that front sides of twocylindrical portions141 and143 that have different inner diameters are connected by aconnection part142 in the radial direction. Here, thehammer140 is made of a metal, which is basically a specification for better performance. It is preferable to make the hammer size as large as possible if the hammer can be housed in thehammer case103, and a diameter (outer diameter) d3 thereof is preferably 44 mm or more. Moreover, the outer diameter of thehammer140 is preferably less than four times the shaft diameter of thespindle130. The twostriking claws146aand146bthat protrude toward the front side (the side of the anvil160) in the axial direction are formed at two opposite positions on the outer peripheral side of thefront surface142awhich is formed by theconnection part142. Thestriking claws146aand146bare equally arranged in a way that the central positions of thestriking claws146aand146bare respectively separated by a rotation angle of 180 degrees when viewed in the rotational direction. Two side surfaces of each of thestriking claws146aand146bin the rotational direction are arranged at predetermined angles in the rotational direction to achieve proper surface contact when colliding with the twoblade parts163aand163bof theanvil160. Thehammer cam grooves144 and145 are formed on the inner peripheral side of thecylindrical portion141 of thehammer140 and on an inner wall portion of a throughhole141awhich faces the outer surface (cylindrical surface) of thespindle130. Here, it can be understood that the throughhole141ais formed with a larger diameter than the throughhole41aof thehammer40 as shown inFIG. 4(1) andFIG. 4(2). Therefore, sufficient lengths of thehammer cam grooves144 and145 in which thecam balls151aand151bmove are ensured. Thehammer cam grooves144 and145 are recesses, which respectively have a substantially trapezoidal contour if the inner peripheral surface of thehammer140 is unfolded into a plane, and form a space that restricts movement of thecam balls151aand151bwith thespindle cam grooves133 and134. In addition,grooves144aand145afor inserting thecam balls151aand151bduring assembly are formed on a portion of thehammer cam grooves144 and145. Because the rotation angle of the hammer is set to two angles, 180 degrees and 360 degrees, in this embodiment, a cam lead angle θ_Mof thehammer140 is set within a range of θ_H1=16-36 degrees such that the cam lead angle θ_Mis a predetermined value. This value is sufficiently low as compared with the conventional impact tool and forms a structure for laying down the cam lead angle. Additionally, the maximum revolution speed of the motor is preferably set to about 18,000-27,000 rpm. In this case, the revolution speed of thespindle130 is 2,100-3,150 rpm.
• Next, a shape of thespindle130 is described with reference toFIG. 16(1),FIG. 16(2), andFIG. 16(3).FIG. 16(1) is a front view of thespindle130,FIG. 16(2) is a side view, andFIG. 16(3) is a cross-sectional view along the section I-I ofFIG. 16(1). Thespindle130 is made of a metal and has a substantially cylindrical shape and is disposed between theanvil160 and thespeed reduction mechanism120. Arear end part139 of thespindle130 in the longitudinal direction is pivotally supported by the bearing119b(refer toFIG. 13(1) andFIG. 13(2)). A diameter d1 of theshaft part131 of thespindle130 is preferably 16 mm or more. Here, the diameter d1 is set to 18 mm to be sufficiently larger than the diameter of thespindle30 shown inFIG. 5(1) andFIG. 5(2). Since thespindle130 is thick, even though the cylindrical internal space is formed hollow to communicate thefitting hole131aon the front end side and thecylindrical hole135aon the rear end side, sufficient strength is ensured. The hollow structure allows the internal space to be filled with grease and facilitates supplying the grease to the anvil side, and therefore is advantageous in terms of lubricity. Two sets ofspindle cam grooves133 and134 are formed on the outer peripheral surface of thespindle130. Here, thespindle cam grooves133 and134 respectively have a substantially V shape in the side view (when viewed in a direction orthogonal to the axis D1), and a cam lead angle ν_S1of each of thespindle cam grooves133 and134 is set to a predetermined angle. In the second embodiment, the cam lead angle θ_H1of thehammer140 and the cam lead angle ν_S1of the spindle are set to be the same in the range of 16-30 degrees, for example, to relatively reduce the cam lead angle θ_M. Even though the cam lead angle θ_H1is reduced, the diameter d1 of thespindle130 is large and the circumferential length is long. Accordingly, the distance for movement of thecam balls151aand151bis increased to ensure a sufficient retreat amount of the hammer140 (hammer back amount).
• On the rear side of theshaft part131 of thespindle130, aplanetary carrier part135 of thespeed reduction mechanism120 is formed. Disk-shapedattachment parts137 and138 are formed on theplanetary carrier part135. Theattachment part137 has a shape formed by connecting a large-diameter part137con the front side and a small-diameter part137d on the rear side. Theattachment part137 extends in a direction orthogonal to the axis D1 and is formed with twofitting holes137aand137bthat are arranged at equal intervals in the rotational direction. Theattachment part138 is disposed in parallel to theattachment part137 on the rear side of theattachment part137 at a predetermined distance from theattachment part137. Theattachment part138 is also formed with twofitting holes138aand138bthat are arranged at equal intervals in the rotational direction and, together with thefitting holes137aand137b, fix theshafts124aand124b(both refer toFIG. 13(1) andFIG. 13(2)) for pivotally supporting theplanetary gears122aand122b. Theshafts124aand124bmay have substantially the same hole diameter (diameter) as the first embodiment. However, in the case of the second embodiment, the positions for forming thefitting holes137a,137b,138a, and138bcause problems. Generally, a drill that moves in parallel to the axial direction from the rear side is used to form thefitting holes137a,137b,138a, and138b. At the moment, in order that the tip of the drill that protrudes toward the front side of theattachment part137 does not process thespindle shaft part131, a diameter S of a circle contacting the innermost peripheral points of thefitting holes137aand137bneeds to be larger than the diameter d1 of thespindle shaft part131. The structure shown inFIG. 5(1) also follows such a positional relationship (refer toFIG. 2). In contrast thereto, in this embodiment, the inner diameter of the diameter S of the circle contacting the innermost peripheral points of thefitting holes137aand137bis configured to be smaller than the diameter d1 of thespindle shaft part131. In other words, the diameter d1 of the spindle130 (the shaft part131) is made larger than the diameter S of the innermost peripheral circle of thefitting holes137aand137b. That is, thespindle130 and thefitting holes137aand137boverlap in the radial direction. In order to realize this positional relationship, agroove part136ais formed on the front side of theattachment part137 by cutting to reduce the outer diameter. During the drilling process performed by using the drill, the tip of the drill does not contact the outer peripheral surface on the side of thespindle shaft part131. The result is that the diameter S of the circle contacting the innermost peripheral points of thefitting holes137aand137bmay be equal to the conventional diameter and does not increase excessively. Thus, even if thespindle shaft part131 has a large diameter, increase of a diameter d2 of theplanetary carrier part135 is prevented. In addition, thegroove part136ais convenient for thegroove part136amay also be used as a space for disposing thedamper156 such as annular rubber. A steppedpart136 having an increased thickness in the axial direction is formed on the front side of theattachment part137, and the rear side surface of thedamper156 is held by the steppedpart136.
• Thespindle130 and thehammer140 are connected by the cam mechanism, and when thespindle130 is driven to rotate, the rotation is transmitted to thehammer140 via the cam mechanism. When the rotation begins and before thehammer140 reaches ½ of the rotation, thestriking claws146aand146bof thehammer140 abut theblade parts163aand163bof theanvil160 and cause theanvil160 to rotate. At the moment, when the engagement counter force from theanvil160 causes relative rotation between thespindle130 and thehammer140, thehammer140 starts to retreat toward the side of themotor104 while compressing thespring154 along thespindle cam grooves133 and134 of the cam mechanism. Then, when the retreat of thehammer140 causes thestriking claws146aand146bof thehammer140 to move over theblade parts163aand163bof theanvil160 to release thehammer140 and theanvil160 from the engagement state, thehammer140 is rapidly accelerated forward and rotated in the rotational direction by the elastic energy accumulated in thespring154 and the function of the cam mechanism in addition to the rotational force of thespindle130.
• When thehammer140 is moved forward by the urging force of thespring154, thestriking claws146aand146bof thehammer140 are engaged with thenext blade parts163band163aof theanvil160 again after the rotation, so as to perform strong striking and thehammer140 and theanvil160 start to rotate integrally. The striking applies a strong rotational force to theanvil160. Thus, a rotational striking force is transmitted to a fastener member, such as a bolt, through the socket (not shown) which is mounted on theattachment part161aof theanvil160. Thereafter, the same operation is repeated to intermittently and repeatedly transmit the rotational striking force from the socket to the fastener member. The above describes a state when thehammer140 performs normal striking on theanvil160. Like the first embodiment, theimpact tool101 of the second embodiment is also configured to perform one-skip striking by setting the rotation speed of themotor104 to a high-speed region of a first revolution speed T₃or more. Moreover, by driving themotor104 in a low-speed region of a second revolution speed T₄or less, theimpact tool101 is able to perform continuous striking Here, the relationship between the revolution speed T₄and the revolution speed T₃is T₄<T₃, and in either the high-speed region or the low-speed region, the revolution speed of thespindle130 may be set to an appropriate value to prevent pre hit or over shoot.
• FIG. 17(1) andFIG. 17(2) are views for illustrating a striking angle during one-skip striking of thehammer140 and theanvil160. Thestriking claw146aof thehammer140 rotates by arotation angle181 to strike theblade part163aof theanvil160 after passing the rear side of theblade part163aof theanvil160. Then, thestriking claw146arotates by arotation angle182 to strike theblade part163aof theanvil160 in the same manner after passing the rear side of theblade part163a. After thestriking claw146bof thehammer140 is disengaged from theblade part163bof theanvil160, thestriking claw146bis engaged with theblade part163bagain without contacting theblade part163a. At the moment, the rotation angle is about 360 degrees. After the relative rotation of therotation angle181 of thehammer140 is performed, the relative rotation of therotation angle182 is performed. Therotation angle181 and therotation angle182 are preferably the same.
• FIG. 18 is a diagram showing a condition of thehammer140 and theanvil160 when the striking is performed based on the striking angle ofFIG. 17(1) andFIG. 17(2). The vertical axis indicates the position of thehammer140 in the front-rear direction, wherein “+” indicates thehammer140 is on the front side while “−” indicates thehammer140 is on the rear side, and the value indicates the distance (mm) 0 indicates a front-side position of thestriking claw146aof thehammer140 during rotation in a stationary or low-load state, and at the moment, a front-side position of theblade part163ais 0 as well. The horizontal axis indicates the relative rotation angle of thehammer140 with respect to theanvil160, wherein one round is 360 degrees. When thetrigger106ais pulled to the full and thespindle130 rotates at a high speed, a predetermined counter force is applied to thestriking claw146aof thehammer140 and when the counter force exceeds the disengaging torque, thehammer140 moves rearward in the axial direction. The retreat amount of thehammer140 with respect to the spindle130 (hammer back amount) is determined by the cam shaft length×2. When the retreat amount of thehammer140 becomes larger than the maximum engagement amount F with theblade part163a(refer toFIG. 13(1) andFIG. 13(2)), thestriking claw146aand theblade part163aare released from the engagement state and thestriking claw146arotates and slips through the rear side of theblade part163aand passes the rear side of thenext blade part163bto strike the following blade part, i.e., theoriginal blade part163a. In the diagram, asolid line171 indicates a locus of movement of a corner part of thestriking claw146aon the axial direction front side and the rotational direction front side while a dottedline172 indicates a locus of movement of a corner part of thestriking claw146aon the axial direction front side and the rotational direction rear side. Thus, in order that thestriking claw146askips thenext blade part163bto strike theblade part163afollowing thenext blade part163bwhen the striking is performed, thespindle130 is rotated at a sufficiently high speed such that thestriking claw146apasses the rear side of theblade part163bwithout contacting theblade part163bbefore thehammer140 that has compressed thespring154 and moved to the rear side returns to the axial direction front side. At the point of the rotation angle of 200 degrees, the axial direction front position of thestriking claw146apasses a portion that is separated from theblade part163aof theanvil160 by 3 mm or more. In addition, althoughFIG. 18 only illustrates thestriking claw146a, thestriking claw146balso performs one-skip striking in the same manner. Therefore, a high striking torque is achieved.
• According to the second embodiment, the back amount of thehammer140 can be increased without increasing the dimensions of thespindle130 in the axial direction and thus, by properly setting the revolution speed of themotor104, one-skip striking can be performed. Furthermore, the outer diameter of thehammer140 is maintained equivalent to the conventional dimension while the inner diameter (the diameter of the spindle130) is increased. Thereby, the inertia of thehammer140 decreases and the hammer is easy to rotate during one-skip striking. Moreover, through control to perform one-skip striking, the maximum revolution speed of the motor is significantly improved in comparison with the conventional speed. The striking force at the moment is (hammer inertia)×(spindle angular speed)̂2 as shown byequation 2 of the first embodiment. Therefore, even though the inertia of thehammer140 is reduced by 10%, for example, when the rotation speed is raised by 30%, the striking force is maintained equivalent to the conventional striking force or higher. Here, it is assumed that the striking energy E of the current product is E=1/2×1.0×1.0̂2=0.50 in (equation 1), when the hammer inertia is set smaller than the current product and the spindle angular speed is set higher than the current product for comparison, the relationship between the angular speed up and the striking energy E is as follows.
• 
  E=1/2×0.9×1.3̂2=0.76 [improved by 1.52 times]  Example 1:
• 
  E=1/2×0.8×1.3̂2=0.68 [improved by 1.36 times]  Example 2:
• 
  E=1/2×0.8×1.5̂2=0.90 [improved by 1.8 times]  Example 3:
• Thus, in the case of performing one-skip striking, an advantage is that even though the hammer inertia is reduced, since the revolution speed is significantly increased, the striking force is greatly enhanced. Moreover, for a specification with a high revolution speed and large hammer inertia, there is a problem that the hammer back amount also increases significantly. Further, when the spring constant of the hammer spring is raised to cope with the aforementioned problem, the disengaging torque increases and impairs the usability. Therefore, in this embodiment, the optimal hammer inertia and motor rotation speed are adopted to achieve a striking force equivalent to or higher than the conventional force without increasing the tool size. In addition, because the disengaging torque at the moment can be reduced as well, the two-claw specification is able to carry out one-skip striking and the impact electric tool achieves both high performance and usability.
• FIG. 19(1) andFIG. 19(2) are views for illustrating the striking angle during continuous striking of thehammer140 and theanvil160. Thestriking claw146aof thehammer140 on the rotation side rotates by arotation angle185 to strike theblade part163bof theanvil160 after passing the rear side of theblade part163aof theanvil160. Then, thestriking claw146aof thehammer140 rotates by arotation angle186 to strike theblade part163aof theanvil160 after passing the rear side of theblade part163bof theanvil160. At the moment, the rotation angle is approximately 180 degrees. Thereafter, the striking of the striking claw of the hammer on the next struck claw is performed in the same manner. Here, therotation angle185 and therotation angle186 are preferably the same. However, the aforementioned “approximately 180 degrees” refers to an angle in a predetermined range.
• FIG. 20 is a diagram showing a condition of thehammer140 and theanvil160 when the striking is performed based on the striking angle ofFIG. 19(1) andFIG. 19(2). The vertical axis and the horizontal axis have the same relationship asFIG. 18. During rotation of thespindle130 in the low-speed mode, a predetermined counter force is applied to thestriking claw146aof thehammer140 and when the counter force exceeds the disengaging torque, thehammer140 retreats. When the retreat amount of thehammer140 becomes larger than the maximum engagement amount F with theblade part163a, thestriking claw146aand theblade part163aare released from the engagement state and thestriking claw146arotates and slips through the rear side of theblade part163ato be engaged with thenext blade part163b. In the diagram, asolid line173 indicates a locus of movement of the corner part of thestriking claw146aon the axial direction front side and the rotational direction front side while a dottedline174 indicates a locus of movement of the corner part of thestriking claw146aon the axial direction front side and the rotational direction rear side. Thus, in order that thestriking claw146ais properly engaged with thenext blade part163bwhen the striking is performed, rotation of themotor104 is controlled to rotate thespindle130 at a low speed, so as to bring thenext blade part163bas thehammer140 that has compressed thespring154 and moved to the rear side returns to the axial direction front side. AlthoughFIG. 20 only illustrates thestriking claw146a, thestriking claw146balso performs the continuous striking in the same manner.
• FIG. 21 is a diagram showing a relationship between the striking energy E and the disengaging torque T_Bof theimpact tool101 of this embodiment. The striking energy E is the energy that thehammer140 has right before thehammer140 strikes theanvil160. Here, it is calculated based on the conditions that the operation amount (pulling amount) of thetrigger106ais at the maximum, the material to be fastened is lauan material (wood), and the repulsion rate is 0.31. The disengaging torque T_B[kg·cm] and the striking energy E [N·m²×(rad/s)²] shown here are the same as the values obtained by theequation 1 andequation 2 of the first embodiment. The plot points shown inFIG. 21 are obtained by respectively plotting the striking specifications of the invention and the conventional technology.FIG. 21 shows the striking energy E and the disengaging torque T_Bin the case where the rotation angle till engagement of thestriking claw146aof the hammer with thenext blade part163bof the anvil after disengagement of thestriking claw146afrom theblade part163ais set to 180 degrees, and the range of a coefficient K are represented as an upper limit coefficient K₃and a lower limit coefficient K₄.A plot group191 indicates the relationship between the striking energy E and the disengaging torque T_Bof the current product available in the market. As described above, according to the conventional technology, in order to further enhance the striking energy E, the spring pressure of thespring154 needs to be increased and consequently the disengaging torque T_Balso increases and impairs the practicality.
• In contrast thereto, in the case when the rotation angle of the impact tool is such that the rotation angle till engagement with thenext blade part163bafter disengagement from theblade part163aof the anvil is 360 degrees, the relationship between a coefficient K_Pand the striking energy E and the disengaging torque T_Bof the impact tool is set as E=K_P×T_B[K₁<K_P], as indicated by aplot group192, the striking energy E can be improved significantly while the disengaging torque is maintained at 7-15 kg·cm, and thus it is possible to obtain high striking energy E in the upper region with respect to the region of the solid line K₃.
• Thus, in this embodiment, the striking mechanism having two striking claws and two struck claws, same as the conventional technology, is used to perform striking in the region where the relationship between the striking energy E and the disengaging torque T_Bsatisfies 15.0×T_B>E>9.3×T_B. Meanwhile, the impact tool is able to perform not only one-skip striking but also continuous striking. The striking energy E in the case of continuous striking is in the relationship as indicated by thearrow192aduring one-skip striking and in the relationship as indicated by thearrow191a(or thereunder) during continuous striking. Therefore, in a case where a low striking torque is sufficient, e.g. fastening particularly short screws into wood, continuous striking is performed so as to carry out the fastening process with an appropriate striking torque.
• FIG. 22 is a diagram showing a relationship between the maximum engagement amount F [mm] and the cam lead angle θ₁[deg] of theimpact tool101 according to this embodiment of the invention. According to the inventors' experiment, the impact tool that has a high disengaging torque T_Band creates a favorable striking feeling is realized by the striking specification that uses the maximum engagement amount F of the anvil and the hammer calculated based on Equation 4: F [mm]=−0.125×θ₁[deg]+6.5, with respect to the cam lead angle θ₁(=θ_H1=θ_S1). Further, at the moment, by significantly increasing the spindle revolution speed to perform one-skip striking, the striking energy E is enhanced significantly as compared with the conventional technology. In addition, if the spindle revolution speed is significantly reduced during transition to the striking operation to perform continuous striking, the feeling from continuous rotating to the start of the striking is improved. Besides, inequation 4, the range of the maximum engagement amount F may be adjusted in a range of ±0.7. The range of the cam lead angle θ₁(=θ_H1=θ_S1) at the moment is preferably about 16-36 degrees.
• Although the invention has been described based on the two embodiments above, the invention should not be construed as limited to the aforementioned embodiments, and various modifications may be made without departing from the spirit of the invention. For instance, the hammer and anvil described above are respectively provided with the same number (two or three) of striking claws and struck claws, but the number of the striking claws of the hammer and the number of the struck claws of the anvil may be changed to other numbers, and the invention is also applicable to an impact tool that the number of the striking claws differs from the number of the struck claws.

Claims (17)

What is claimed is:

1. An electric tool, comprising:

a motor;

a spindle driven in a rotational direction by the motor;

a hammer relatively movable in an axial direction and the rotational direction in a predetermined range with respect to the spindle and urged forward by a cam mechanism and a spring; and

an anvil disposed rotatably in front of the hammer to be struck by the hammer when the hammer rotates while moving forward,

wherein a relationship between a striking energy E, which the hammer has right before the hammer strikes the anvil, and a disengaging torque T_B, which is applied between the hammer and the anvil right before the hammer is disengaged from the anvil, is set as E>5.3×T_B.

2. The electric tool according toclaim 1, wherein the hammer comprises three striking claws that are arranged equally in the rotational direction while the anvil comprises three struck claws that are arranged equally in the rotational direction, and

a range of a relative rotation angle of the hammer with respect to the anvil from when the hammer strikes the anvil till the hammer strikes the anvil again after the hammer stroke the anvil and moved rearward is set to substantially 240 degrees.

3. The electric tool according toclaim 2, wherein the relationship between the striking energy E, which the hammer has right before the hammer strikes the anvil, and the disengaging torque T_B, which is applied between the hammer and the anvil right before the hammer is disengaged from the anvil, is set as 5.3×T_B<E<9.3×T_B.

4. The electric tool according toclaim 3, wherein when a maximum engagement amount, which is an engagement length of the anvil and the hammer in the axial direction when the anvil is at a foremost position, is set to A [mm] and a cam lead angle, which is a lead angle between cams disposed on the hammer and the spindle such that the hammer retreats when the hammer rotates relatively with respect to the spindle, is set to θ [deg], a relationship between A and θ is set as (−0.125×θ+7.5)−0.7<A<(−0.125×θ+7.5)+0.7.

5. The electric tool according toclaim 4, wherein an overlapping length of the striking claws and the struck claws in the axial direction when a counter torque received from a tip tool mounted on the anvil is small is 2.3 mm-5.0 mm, and lead angles θ of a cam groove of the hammer and a cam groove of the spindle are made equal and set as θ=26-36 degrees.

6. The electric tool according toclaim 5, wherein a diameter of the hammer is 35 mm-44 mm and an inertia of the hammer is 0.39 kg·cm²[0.00038 N·m²] or less.

7. The electric tool according toclaim 6, wherein a diameter of the spindle is 10 mm-15 mm and a spring constant of the spring is 40 kgf/cm or less.

8. The electric tool according toclaim 3, comprising a trigger switch adjusting a rotation speed of the motor,

wherein when the trigger switch is pulled to a maximum or to an extent close to the maximum, the rotation speed of the spindle is adjusted such that the striking claw moves over the next struck claw to strike the struck claw following the next struck claw, and

when the trigger switch is pulled slightly, the rotation speed of the spindle is adjusted such that the striking claw strikes the next struck claw when the hammer retreats to disengage the striking claw from the struck claw and rotates.

9. The electric tool according toclaim 1, wherein the hammer comprises two striking claws that extend in opposite directions while the anvil comprises two struck claws at opposite positions, and

a range of the relative rotation angle of the hammer with respect to the anvil from when the hammer strikes the anvil till the hammer strikes the anvil again after the hammer stroke the anvil and moved rearward is set to substantially 360 degrees.

10. The electric tool according toclaim 9, wherein the relationship between the striking energy E, which the hammer has right before the hammer strikes the anvil, and the disengaging torque T_B, which is applied between the hammer and the anvil right before the hammer is disengaged from the anvil, is set as 9.3×T_B<E<15.0×T_B.

11. The electric tool according toclaim 10, wherein when a maximum engagement amount, which is an engagement length of the anvil and the hammer in the axial direction when the anvil is at a foremost position, is set to F [mm] and a cam lead angle, which is a lead angle between the cams disposed on the hammer and the spindle such that the hammer retreats when the hammer rotates relatively with respect to the spindle, is set to θ₁[deg], a relationship between F and θ₁is set as (−0.125×θ₁+6.5)−0.7<F<(−0.125×θ₁+6.5)+0.7.

12. The electric tool according toclaim 11, wherein an overlapping length of the striking claws and the struck claws in the axial direction when a counter torque received from a tip tool mounted on the anvil is small is 2.3 mm-5.0 mm, and lead angles θ₁of a cam groove of the hammer and a cam groove of the spindle are made equal and set as θ₁=16-30 degrees.

13. An electric tool, comprising:

a motor;

a spindle driven in a rotational direction by the motor;

a hammer relatively movable in an axial direction and the rotational direction in a predetermined range with respect to the spindle and urged forward by a cam mechanism and a spring;

an anvil disposed rotatably in front of the hammer to be struck by the hammer when the hammer rotates while moving forward; and

a trigger switch adjusting a rotation speed of the motor,

wherein when the trigger switch is pulled to a predetermined extent or more, the electric tool performs one-skip striking that a striking claw of the hammer moves over a next struck claw of the anvil to strike a struck claw following the next struck claw, and

when the trigger switch is pulled less than the predetermined extent, the electric tool performs continuous striking that the striking claw strikes the next struck claw.

14. An electric tool, comprising:

a motor;

a spindle driven in a rotational direction by the motor;

a hammer comprising two striking claws, wherein the hammer is relatively movable in an axial direction and the rotational direction in a predetermined range with respect to the spindle and urged forward by a cam mechanism and a spring;

an anvil comprising two struck claws and disposed rotatably in front of the hammer to be struck by the hammer when the hammer rotates while moving forward; and

a trigger switch adjusting a rotation speed of the motor,

wherein an outer diameter d1 of a shaft of the spindle is 16 mm or more and an outer diameter d3 of the hammer is less than four times the outer diameter d1, and

a lead angle between cams disposed on the hammer and the spindle is set to 16-30 degrees.

15. The electric tool according toclaim 14, wherein the electric tool performs one-skip striking that the striking claw moves over the next struck claw to strike the struck claw following the next struck claw.

16. The electric tool according toclaim 14, wherein the spindle has a cylindrical shape, in which an internal space communicates a front end with a rear end.

17. The electric tool according toclaim 14, wherein a plurality of fitting holes are formed on a motor side of a shaft part of the spindle to pivotally support a planetary gear of a planetary gear speed reduction mechanism, and

a diameter S of a circle contacting an innermost peripheral point of the fitting hole is formed smaller than the outer diameter d1 of the shaft of the spindle.

Images